The invention relates to a method for evaluating an output signal of a device which senses cyclical motion, in particular, a method applicable to evaluation of an output of a sensing device for determination of rotational speed.
A system employing an evaluation method of this type is disclosed, for example, in EP 0 684 480 A1 (U.S. Pat. No. 5,606,252). The known system evaluates a signal which is emitted by a sensing device used for the determination of the rotational speed of a rotating part. When such devices are used in a vehicle, the rotating parts monitored are generally the wheels, the rotational speeds of which are used, for example, as input signals for an anti-lock brake system (ABS).
In a sensing device upon which the known evaluation method is based, a pulse wheel having a series of teeth is mounted on the rotating part. The pulse wheel, referred to also as a pole wheel particularly in connection with sensing devices employing inductive action, is actively coupled with an inductive sensor attached on a fixed part which inductively produces a periodic signal during rotation of the pole wheel. When the rotational speed remains constant, the signal produced by the sensor has a,constant frequency due to an equidistant placement of the teeth on the pole wheel. The actual rotational speed of the rotating part is directly related to the frequency of the inducted signal, which may be determined following suitable conversion.
The above signal is normally transmitted to an electronic control device for evaluation. The evaluation process is then carried out in the form of a program sequence in a microprocessor located in the control device.
In sensor systems of the type described above, damage to the pole wheel may result in generation of irregular signals despite a constant rotational speed of the measured part. A pole wheel may be damaged, for example, as a result of an accident, such that one or more teeth,may be missing. Consequently, signal cycles in the output signal of the sensor or in the signal received by the control device will be missing. In accordance with conventional evaluation methods, an undesirable alteration in the rotational speed derived from the received signal may result.
It is therefore an object of the invention to provide a method for evaluating an output signal of a device sensing cyclical motion, in accordance with which abnormal signal evolutions occurring as a consequence of damage to the sensor device are recognized and displayed in a reliable manner.